Heating devices in which the heating coil is covered with cast copper or brass are known. These cast heating cartridges typically have an external casing of stainless steel, but have the disadvantage of relatively great heat dissipation through the casing's outer surface. As a result, adjacent components which actually do not need any heating are heated, which has a detrimental effect when considering the overall energy balance.
A typical prior art heating device is disclosed in EP-A-0468483. This reference describes a heating device for a hot runner nozzle, which is surrounded alternately by a plurality of layers of stainless steel and ceramic insulating material. The layers may be provided in different thicknesses. Such a heating device is relatively complex to produce and is not optimal with regard to its insulating effect.